Hibernate Criteria Order By

Question

I have a table called Gift, which has a one-to-many relationship to a table called ClickThrough - which indicates how many times that particular Gift has been clicked. I need to query for all of the Gift objects, ordered by ClickThrough count. I do not need the ClickThrough count returned, as I don't need anything done with it, I just want to use it for purposes of ordering.

I need the query to return a List of Gift objects directly, just ordered by ClickThrough count. How do I do this using the Criteria API? I can find a lot of documentation out there on similar information to this, but nothing quite like what I need.

Answer 1

If you want to return a list of entities or properties in combination with a count you will need a group by. In criteria this is done through ProjectionList and Projections. e.g.

    final ProjectionList props = Projections.projectionList();
    props.add(Projections.groupProperty("giftID"));
    props.add(Projections.groupProperty("giftName"));
    props.add(Projections.count("giftID"), "count"); //create an alias for the count
    crit.setProjection(props);

    crit.add(Order.desc("count")); //use the count alias to order by

However, since you're using ProjectionList you will also need to use AliasToBeanConstructorResultTransformer.

Answer 2

Note for anyone else that comes through here looking to order by a property/column:

When using the approaches mentioned here, no results were found. The fix was to use criteria.addOrder(Order.asc(property)); instead. Notice the difference is to use addOrder, rather than add;

I've had this issue several times after running here for a quick reference.

Answer 3

You have a one-to-many relationship from Gift to ClickThrough so I assume each ClickThrough is a record with some datetime or other information associated with it. In this case, I would add a "count" field to your mapping file and attach the ordering to the criterion:

criterion.add(Order.asc(count)))

The mapping property looks something like:

<property name="count" type="integer" formula="(select count(*) from Gift g inner join ClickThrough ct on ct.gift_id=g.id where g.id=ID)"/>

If you can't or don't want to change the mapping file, you could use Collections.sort() with a Comparator though it seems less efficient having to return so much data from the DB.